​UTC to test hybrid-electric propulsion system on Dash 8

United Technologies install a hybrid-electric propulsion demonstrator system on a modified Bombardier Dash 8-100 and conduct test flights by 2022.

An electric motor will support one of the aircraft's turboprop engines during take-off and climb.

Project 804, as it is known, will be led by United Technologies Advanced Projects – the group's new rapid prototyping and development unit – and draw on the expertise of UTC companies Collins Aerospace and Pratt & Whitney.

The project name references the straight-line distance in miles between P&W's Canadian facility in Montreal and a Collins Aerospace site in Rockford, Illinois.

UTC says that the arrangement allows the use of a smaller-than-usual gas turbine engine, optimised for cruise efficiency. The overall system could deliver fuel savings of “at least 30%” during a 1h flight, it adds.

Half of the propulsion system’s power output during take-off and climb will come from the gas turbine, with the balance provided by an electric motor; the two powerplants will jointly drive the propeller via a gearbox.

UTC says the propulsion system will generate 2MW for the 40-seat demonstrator. By comparison, the Collins Aerospace electrical system on the Boeing 787 – which UTC describes as “the most-electric airplane in the sky today” – generates around 1.5MW.

The engine architecture could be "suitable" for both newly designed aircraft and as a retrofit option for in-service turboprops, says UTC. But it stresses that the fuel savings will partly come from the latest gas turbine technology, rather than solely from added electrification.

UTC opted to pursue an electrical-assist architecture because the "high-power and short-duration" requirement for electric propulsion enables the energy storage requirement to be accommodated "within the aircraft's maximum take-off weight”, it says.

But installation of the hybrid-electric system will still increase the Dash 8's operating empty weight and approximately halve the aircraft's fuel capacity, leading to a 400nm (740km) range reduction, to around 600nm.

However, UTC argues that in light of the targeted fuel savings the trade-off "makes both technical and economic sense" as the vast majority of missions flown by Dash 8-100s are shorter than 500nm.

A clean-sheet design could "significantly reduce the weight and range penalty by better integrating the [hybrid-electric] system with the airframe structure and required secondary systems".

The group acknowledges that a serial hybrid-electric system – where a hydrocarbon fuel-powered engine generates electricity to drive electric motors – could deliver "potentially significant advantages" in terms of overall aircraft efficiency.

But UTC argues that such an architecture would be "contingent on the aircraft original equipment manufacturers' willingness to deviate from the conventional tube-and-wing configuration".

A full-electric architecture has been dismissed as an option for a Dash 8-sized aircraft because, based on current technology, the weight of the required batteries alone would exceed the maximum take-off weight, UTC says.

"Given the large energy needs of even short-haul missions, and near-term energy storage densities, a fully electric solution to propel a regional turboprop-sized aircraft is out of reach for the short- to mid-term future," the group says.

The project's objective is to deliver scaleable technology that could be used for platforms ranging from general aviation to large commercial jets, and to accelerate development of suitable batteries, electric motors and power management systems.

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